1. Field of the Invention
The invention relates to a semiconductor device that comprises a transistor with high ESD (Electro Static Discharge) capability and high noise capability including EMC (Electro Magnetic Compatibility).
2. Related Art
Conventionally, integrated intelligent switch devices, which are the result of integrating a plurality of power semiconductor elements (switch elements) and a drive control circuit and so forth on the same chip, are used in automobile electrical components, a variety of industrial machinery, motor control, OA (Office Automation) devices, mobile (portable) devices or domestic electrification devices, and so forth, which require high ESD capability and high noise capability including EMC.
Integrated intelligent switch devices are such that a surge absorption element is formed on the same semiconductor substrate in order to protect each element in the device from surge voltages, noise, and so forth. See Japanese Patent Application Laid-Open No. H3-49257 (third figure, for example).
FIG. 3 is a cross-sectional view of a constitution in which a lateral MOSFET and a vertical-type diode, which is a surge absorption element, are formed on the same semiconductor substrate. As shown in FIG. 3, a lateral power MOSFET 20 and a vertical-type diode 30, which is a surge absorption element, are formed on a semiconductor substrate 10.
The semiconductor substrate 10 consists of a low concentration N layer 12 on a high concentration N layer 11. P-wells 21 and 31 are formed in the surface region of the low concentration N-layer 12. The lateral MOSFET 20 is formed in the P-well 21. The vertical-type diode 30 is formed in the P well 31.
The surface of the P-well 31 is connected to an anode electrode 33 via the high concentration P layer 32. The anode electrode 33 is connected by wiring 35 to the source electrode 27 of the lateral MOSFET 20, which is connected to the surface of the P-well 21 via a high concentration N layer 24. The lateral MOSFET 20 has a gate electrode 26 and a drain electrode 25.
An electrode 13 is formed on the rear surface of the semiconductor substrate 10. The electrode 13 serves as a cathode electrode of the diode 30. The electrode 13 is connected to the drain electrode 25 of lateral MOSFET 20 by wiring 26 In the constitution of FIG. 3, when an ESD or surge, or the like, is applied to the drain electrode of the lateral MOSFET 20, the energy of the ESD or surge is absorbed by the vertical-type diode 30 to protect the lateral MOSFET 20.
However, when the above device is used in an automobile application in which there are strict demands with regard to ESD capability and surge/noise capability, an extremely high ESD capability of 10 kv to 15 kv (test conditions 150 p F, 150Ω) is required, and, more particularly in a power semiconductor element, a high ESD capability with a typical ESD capability of 25 kv or more is required.
When the above requirements are not satisfied by a power IC equipped with a MOSFET or the like, there is a need to adapt elements such as condensers, diodes, resistors, and so forth as external discrete devices. Thus, there are problems such as an increase in the number of parts, an increased number of operating steps for assembly or the like, and increased costs. On the other hand, by adopting the constitution shown in FIG. 3, external parts can be eliminated.
However, in order to satisfy the desired surge absorption capacity, the surge absorption element that satisfies the above requirements is formed to afford this capacity scope. Thus, the chip area is larger. The increase in the surface area of the surge absorption element in integrating a plurality of elements in one chip, raising the withstand voltage, and reducing the chip area through increased intricacy is a major problem in efforts to reduce the chip-area and costs.